Etching precious metals



vretenait Dec. z, i930 UNITED l STA-TES. PATENT OFFICE JAMES C. MCFABLAND, OF FORT THOMAS, KIENTUCKY, ASSIGNO TO THE WADBWOBTH WATCH CASE CO., OIE' DAYTON, `KENTUCKY, CORPORATION OF KENTUCKY ETCHING PRECIOUS METALS Application med June 22, 1928. Serial VIlo. 87,55`i8.

This invention relates particularly-to a method for etching precious metals; and the `primary 'object is toprovide a simple and efficacious method for the purpose indicated.

In the improved method, chromium platyio 2 ferred method in which chromium plating is applied to the surface; Fig. 2 represents a further step in which a suitableresist design is applied to the chromium plating; Fig. 3 represents a further step in which thechromium plating is removed at the exposed areas; Fig. 4 represents a further step in which the resist is removed; Fig. 5 represents a further step in Which the exposed surfaces of the precious metal are etched While the chromium plating design serves asa resist; Fig. 6 represents the first step in a modified procedure, in which a suitable resist design is applied to the surface of the precious metal; Fi 7 represents a second step in which the chromium plating is applied to the exposed areas of the precious metal;

after removal of the chromium plate throughout the exposed areas thereof; and A2 designates the body.

Referring to Figs. 6-10, D designates a precious metal body; E designatesy a suitable resist designapplied thereto; F designates a chromium plating design applied to thev exposed areas of theprecious metal surface; and D designates the etched areas of the precious metal body.

The process is applicable to the decoration of the surfaces of various precious metals, such as gold, silver, platinum or their alloys. In the preferred procedure illustrated in Figs. 1-5,'the ent-ire precious metal surface to be treated is first plated with chromium; a suitable resist design is then applied to ,the chromium plating; the chromium plating is then removed at the exposed areas, as by means of dilute hydrochloric acid, or dilute sulphuric acid; th resist is then removed; and the precious metal surface is then etched by means of a suitable etching agent. For example, a suitable cyanide solu- 1 tion may be used for etching gold. During t-he etching operation, the chromium plating serves as a resist. After the etching operation, the chromium plating may be removed, if desired. 'The etched blank may then be further decorated in any desired manner. If one so desires, the etched gold surface, for example, may be plated with platinum; and

the chromium plating design may afterwards be removed.

The modified method illustrated in Figs. 6-10 will be understood without further description.

In lieu of chromium plating, lead may be used, if desired. Where-lead is so used, nitric acid may be employed to remove it after the lead has served as a resist in the etching of the gold surface for example.

Where a chrqfnium plating design'is used as a resist in the etching operation, the chromium plating may be allowed to' remain, if desired. Such a plating'is hard, resistant, will not tarnish, and possesses a color somewhat similar to the color .of aluminum.

The resist may be applied to the metal surface in any desired manner. Preferably, the

etched areas of the precious metal t metal surface is coated with a light-sensitive varnish; the film is then acted upon b light transmitted through a transparency aving thereon a picture, design, or character; and the unreacted portions of the varnish are then removed by a suitable developing operation.

Chromium p lating is hard, resistant, and free from tarnishing.

It has been demonstl-ated that it will serve effectively as a resist against those agents which can be used in etching gold and other precious metals and alloys. It is preferred to use chromium' plating rather than lead plating, or some other metal platin as a resist in etching precious metal suraces. It may be added that chromium plating is much superior to ordinary resists for use in etching precious metal surfaces.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, but the appended claims should be construed as broadly as permissible, in view of the prior art.

What I regard as new, and desire to secure by Letters Patent, is: v

1. The method of etching precious metals,

which comprises: applying to the surface ofthe metal a chromium plating adapted to serve as a resist to the etching fluid for the precious metal; etching the exposed surface of the precious metal while said plating design serves as a resist; and removing the chromium plating.

2. The method of etching precious metals :which comprises: applying to the surface of the metal a'chromium plating adapted to serve as a resist to an etching fluid for the Y precious metal; and etching the exposedl surface of the precious metal while said plating design serves as a resist.

3. The method of etching precious metals* which comprises: applying a suitable resist to the precious metal, plating the exposed surface of the precious metal with chromium, Y

removing the resist, etching the exposed surface of the precious metal While the chromium serves as a resist, and removing the chromium.

JAMES C. MCFRLAND. 

